1. Field of the Invention
The present invention relates to an improvement in an axial flow type laser oscillator to be used for laser cutting machines or the like.
2. Description of the Related Art
The following, is an explanation of the prior art axial flow type laser oscillator. As shown in FIG. 3, a prior art axial flow type laser oscillator comprises a gas blower 1, gas cooling units 2a and 2b provided at an inlet port and an outlet port of the gas blower 1, an output mirror 3, a total reflecting mirror 4, gas discharge tubes 5a and 5b, a discharge power supply 6 (e.g. D.C. power source or radio frequency oscillator), gas supply tubings 7a and 7b, gas outlet tubing 8, a rolling slider 11, a gas outlet block 13, an output mirror holder 25a, a total reflecting mirror holder 25b, resonator supporting rods 26a and 26b, gas feeding blocks 27a and 27b, and a resonator supporting metal block 28.
The mutual relations and actions of the above-mentioned structural elements of prior art axial flow type laser oscillator are explained below. As shown in FIG.3, the holder 26a and 26b respectively for holding the output mirror 3 and the total reflecting mirror 4 are mounted at both ends of the resonator supporting rods 26a and 26b. The output mirror 3, the total reflecting mirror 4, the gas discharge tubes 5a and 5b are all placed in a manner such that they are arranged on a common axial line. A gas laser medium is supplied to the two gas discharge tubes 5a and 5b at an equal flow rate from the gas supply tubings 7a and 7b by the gas blower 1 through the gas feeding blocks 27a and 27b, which are attached to the mirror holders 25a and 25b, respectively. The gas supplied to the gas discharge tubes, as described above, is excited by the discharge, which takes place in the gas discharge tubes caused by the current fed from the discharge power supply 6. A laser output light, which is not shown in the drawing, is issued through the output mirror 3. The gas laser medium, which is heated by the discharge and passed through the gas discharge tubes 5a and 5b, is collected at the gas outlet block 13, which is located at the center of the resonator. The gas laser medium is led out of outlet block 13 through the gas outlet tubing 8. The led out gas laser medium is cooled at the gas cooling unit 2b connected in the gas outlet tubing 8 and then returned to the gas blower 1.
The gas laser medium having passed through the gas discharge tubes 5a and 5b is cooled at the gas cooling unit 2b located at the inlet port of the gas blower 1. Therefore, the gas laser medium temperature at the outlet port of the gas cooling unit 2b becomes close to that of the coolant, such as water, which is supplied to the gas cooling unit. However, for cooling the gas laser medium which is heated up by the discharge at a time of constant operation sufficiently after starting the discharge, the temperature of the coolant rises substantially in proportion to the amount of energy exchanged from the gas laser medium to the coolant. Accordingly, the temperature of the gas laser medium at the outlet port of the gas cooling unit 2 rises by an amount of temperature rise of the coolant.
As a result, temperature variations of normally between 3.degree. to 5.degree. C. appear on the gas laser medium temperature at the outlet port of the gas cooling unit 2b caused by the presence or absence of the discharge, although it depends also upon the heat capacity of the coolant and the discharge input. Because this temperature variation remains even after the gas laser medium passes through the gas blower 1 and the gas cooling unit 2a, at a time when the laser oscillator is turned on, or at a time when the discharge input power is changed for adjusting the laser output power, expansion or contraction takes place on the gas supply tubings 7a and 7b owing to the temperature variations of the gas laser medium passing through the gas supply tubings 7a and 7b.
Expansions and contractions taking place on the gas supply tubings 7a and 7b propagate up to the mirror holders 25a and 25b. Consequently, if any non-uniform expansions and contractions on the gas supply tubings 7a and 7b are present, there arises the problem that the optical axis of the resonator deviates and hence the laser output power level fluctuates.